This invention relates to polymer processing systems which treat amorphous polyester to achieve crystallization followed by solid phase polymerization, followed by cooling. An example of such a system is found in Herron Patent No. 4,161,578.
In systems of the type contemplated by this invention, cold amorphous polymer material is fed to a crystallizer and, after substantial heat input, hot product is discharged. The particular apparatus for achieving the crystallization may comprise an indirect heat supply unit or a fluid bed. The SOLIDAIRE.RTM. or TORUSDISC.RTM. equipment manufactured by Hosokawa Bepex Corporation of Minneapolis, Minn. is an example of an indirect heat supply unit which may be utilized for achieving the crystallization. In such a system, steam or other heated fluid is passed through rotors and/or jackets which are in contact with the agitated polymer material. The polymer is thereby heated to the necessary temperature for achieving the crystallization reaction.
In a fluid bed system, for example units manufactured by Hosokawa Bepex, heated air is brought into contact with the polymer material in order to improve heat transfer and to achieve the temperatures required for the crystallization reaction.
In systems of the type described, the crystallized material is transferred to a reactor for achieving polymerization. Subsequent to the polymerization, the material is transferred to a cooler which may also comprise, for example, a TORUSDISC.RTM. or fluid bed system. Where a fluid bed cooler is employed, it has been the practice to achieve the cooling, at least in part, by contacting the hot material with cool gas which may be air or some other gas such as nitrogen. As a result, the gas is heated considerably and may then be recirculated only if first cooled. The expense of cooling is, however, only warranted where nitrogen or some other more expensive gas is being used.